Controlling the quantum interface between two bosonic modes is essential in countless implementations of quantum information processing. However, full controllability is rarely achieved in most platforms due to specific physical limitations. In this talk, I will first introduce the linear two-mode interfaces and the limitations of implementing them in some physical platforms. Then, I will present our systematic strategies to engineer an arbitrary linear two-mod interfaces with the platform-available interfaces and single-mode operations.

Our scheme is developed by completely characterizing the linear two-mode interfaces under the most pessimistic restriction that only single-mode operation is available. We studied two practical situations: 1) When arbitrary single-mode operations can be applied to both modes, we find that every interface can be characterized by an invariant transmission strength; 2) When squeezing is restricted in one of the modes, we discover two additional quantities, irreducible squeezing and irreducible shearing, that are invariant under the allowable controls. By using this characterization, we develop systematic strategies to engineer an arbitrary interface through cascading multiple fixed platform-available interfaces. Without squeezing restriction, our protocol is optimal and requires at most three platform-available interfaces. Under the squeezing constraint, our protocol can be extended to engineer also the additional invariants by using no more than two more rounds of cascade. We also propose the remote squeezing scheme to tackle the squeezing restriction through interfacing with an active auxiliary mode.
 

Please contact phweb@ust.hk should you have questions about the talk.